P3847Risk of stroke overall and by stroke severity among newly diagnosed non-valvular atrial fibrillation patients initiating treatment with rivaroxaban versus warfarin

Background: Standard of care for stroke prevention in patients with non-valvular atrial fibrillation (NVAF) is oral anticoagulation (OAC) therapy. However, the effectiveness of rivaroxaban versus warfarin in risk reduction by stroke severity has not been studied in real-world settings. Purpose: To compare stroke risk (overall and by severity) between rivaroxaban- and warfarin-initiated NVAF patients. Methods: This retrospective cohort study (2011–2017) included de-identified patients from the Clinformatics® Data Mart Database who initiated rivaroxaban or warfarin treatment within 30 days following first NVAF diagnosis. Prior to NVAF diagnosis, patients were required to have 6 months continuous health plan enrollment, CHA2DS2-VASc score ≥2, no history of prior stroke or transient atrial fibrillation, and no prior OAC use. Rivaroxaban and warfarin patients were followed from treatment initiation until the earliest occurrence of a primary inpatient diagnosis of stroke, death, end of health plan enrollment, or end of study. Patients with ischemic or hemorrhaging stroke defined by ICD-9/-10 codes were included in the study. Stroke severity was determined by the National Institutes of Health Stroke Scale (NIHSS) score, imputed by 127 clinically relevant features selected by a random forest method from our previous study. Cox proportional hazard regression, with adjustment for treatment duration and baseline risk factors, was used to compare stroke risk (overall stroke and by severity) in rivaroxaban- versus warfarin-initiated patients.